This invention relates to the continuous treatment of textile and similar webs of material in general and more particularly to an improved method and apparatus for applying a foam treatment medium to textile and similar webs.
A method for the continuous treatment of a web of material of textiles or paper, particularly a dyeing treatment, by applying foam is known from DE-OS 27 22 082. The foam is applied directly to the substrate by means of a nozzle. Although it may be possible to satisfactorily apply large amounts of liquids in the form of foam to a web of material in this manner, it is not suitable for particularly small amounts of liquid because, the unavoidable variations of the amount of liquid applied by the nozzle to a given point of the web of material and also the local variations in the absorptivity of the web of material for the liquid, can lead to considerable relative differences in the coverage of the web of material, which manifest themselves in distinctly visible differences in the depth of the color upon dyeing. Even a later wiping off or squeezing off, as is described in U.S. Pat. No. 2,719,806 for the preparation of coatings, cannot bring, according to experience, aequate uniformity of the application for the dyeing process.
From U.S. Pat. No. 2,795,207, a coating arrangement is known, in which two cylinders are disposed opposite and parallel to each other at the same height and at an adjustable spacing. The web of material runs over the one cylinder, through the gap between the cylinders and around the lower part of the second cylinder. In the upper corner between the two cylinders, a foam feeding arrangement is provided which delivers the foam into the gap between the two cylinders so that it lies, on the one hand, on the surface of the second cylinder and, on the other hand, on the side of the web facing the former. The foam is fed in approximately at the height of the point at which the web of material is transferred from the first cylinder to the second one. The foam layer remains between the web of material and the second cylinder and separates from the second drum again after having travelled through a loop angle of about 180.degree. with the web.
This design is intended for the preparation of coatings of the web of material with foam rubber, where the coating is to be maintained as a layer having a thickness of its own. Slight variations in the feeding of the foam do not matter here because they are mechanically equalized by the subsequent revolution about the second cylinder. In an attempt to dye with this known design, however, the unavoidable local differences in foam feeding would manifest themselves in a different coverage of the web of material with dyeing liquid, which leads to a non-uniform depth of color. This is true particularly because the foam is applied directly to the web of material and is accepted by the latter immediately. A non-uniform amount of dyeing liquid once accepted by the web of material through capillary action between the fibers or even by an initial partial drawing up onto the fibers can no longer be equalized subsequently, contrary to the case of a coating of a type which can later be equalized mechanically and which is to remain standing as a layer but is not to penetrate into the web of material.